Due to explosive increase in communication capacity, attention is given to arrayed elements arranged spatially in parallel, and particularly to a surface emitting laser element array having elements that are easy to array. As the surface emitting laser elements, those having a threshold current of about sub mA are brought into practical use for realization of high-reflective multilayer reflector (DBR: distributed Bragg reflector) or development of a current confinement structure by ion implantation or selective oxidation. Also with development of material for each wavelength, surface emitting lasers for light of various wavelengths are in practical use. Meanwhile, as to speedup, reduction in parasitic capacitance, reduction in electric resistance, increase in differential gain due to optimization of active layer materials, structure and property and low threshold values enable realization of high-speed elements exceeding 10 Gbps.
Meanwhile, when the surface emitting laser elements are arrayed to perform parallel transmission, there occur a problem of various cross talks between the elements, and particularly, of electrical cross talks. To solve this problem, the technique for preventing electrical cross talks is disclosed (for example, in the patent documents 1 and 2).
According to the above-mentioned patent documents 1 and 2, electrical isolation between the elements is maintained by using a semi-insulating substrate and separation grooves for isolation formed by etching or doping a buffer layer with chromic oxide or the like by the same method as the method for manufacturing the semi-insulating substrate.
[Patent Document 1] U.S. Pat. No. 7,061,956, specification.
[Patent Document 2] Japanese Patent Application Laid-open No. 11-261174.